A typical strap fastener includes a base, a reel pivotal on the base, a lever pivotally installed on the reel, two ratchet wheels secured to the reel, a first detent movably installed on the base for engagement with the ratchet wheels and a second detent movably installed on the lever for engagement with the ratchet wheels. In use, a first strap or a first end of a strap is tied to the base. A second strap or a second end of the strap is wound on the reel. The lever is pivoted relative to the base in order to perform a one-way rotation of the reel through cooperation of the detents with the ratchet wheels. The reel winds the first strap or the first end of the strap so as to exert a tensile force on the straps or the strap. The tensile force may however be too large for the straps or the strap to sustain. In such a case, the straps or the strap may be fractured. When that happens, cargo will get loose and become vulnerable to damage. What is worse is that the loose cargo may hurt people.
The present invention is therefore intended to obviate or at least alleviate the problems encountered in the prior art.